The Department of Justice (DOJ) Antitrust Division on Tuesday said it had expanded its investigation into beef affordability to include eight of the largest grocery retailers in the United States.

The expansion comes after the DOJ launched an antitrust probe in May into the "Big Four" meatpackers - JBS, Cargill, Tyson Foods and National Beef - which the department said control more than 85% of the U.S. beef processing market.

Tuesday's announcement expands the federal government's scrutiny to the retail level of the food supply chain.